1. Field of the Invention
The present invention relates to an image-sensing apparatus. More specifically, the present invention relates to an image-sensing apparatus (a main component of a digital camera, video camera, or camera incorporated in or externally fitted to a digital video unit, personal computer, mobile computer, cellular phone, personal digital assistant (PDA), or the like) that optically takes in an image of a subject through an optical system and that then outputs it in the form of an electrical signal by means of an image sensor, and in particular to an image-sensing apparatus provided with a compact high-zoom-ratio zoom lens system that covers from a wide-angle range to a telephoto range.
2. Description of the Prior Art
In zoom lens systems that cover from a wide-angle range to a telephoto range, high zoom ratios and compactness are eagerly sought. As zoom lens systems of this type, there are conventionally known five-unit zoom lens systems of positive-negative-positive-positive-positive and positive-negative-positive-negative-positive types. In these zoom lens systems, the first lens unit is kept stationary during zooming, and focusing in close-up shooting is achieved by moving the succeeding lens units. This helps avoid excessive enlargement of the front lens diameter. On the other hand, Japanese Patent Application Laid-Open No. H8-2483118 proposes a four-unit zoom lens system of a positive-negative-positive-positive type wherein the optical path is turned with a prism inserted between lenses to make the zoom lens system compact along its optical axis.
In recent years, as image sensors are made increasingly small, further miniaturization has been sought in zoom lens systems. This, however, cannot be achieved with the five-unit zoom constructions mentioned above. On the other hand, the zoom lens system proposed in the patent publication mentioned above has a large number of lenses, and neither its optical performance nor its compactness along the optical axis is satisfactory.